1. Field of the Invention
The present invention relates to a novel process to extract pectin from a waste hull/hypocotyl stream during soybean processing and to a whitened form of soy pectin.
More particularly, the present invention relates to a novel process to extract pectin from waste soybean hull/hypocotyl streams using a chemical extraction agent in addition to heat and agitation followed by precipitation in alcohol, drying and whitening and to a whitened soy pectin product.
2. Description of the Related Art
US farmers produce about half of the 140 million metric tons of soybeans produced worldwide each year (Klugh 1997, Am. Soybean Assoc. 1998). All but 1 million metric tons are oil type beans that are crushed and made into soybean oil for human food products or soybean oil as an industrial feed stock. The defatted soybean meal is used mainly for animal feed. Oil soybeans are composed of about 90% cotyledons, 8% hulls and 2% hypocotyls. Soybean hulls and about 40% of the hypocotyls are sold separately for $0.07 to $0.08/kg and are referred to as soy “mill run” for use as animal feed. Mill run is about 95% hulls that are composed mostly of alpha cellulose and hemicellulose; they contain about 9% protein and are low in lignin. The digestible energy of soy hulls is essentially equal to grains for ruminant animals (Liu 1997). The soy hull pectins of this invention are suitable as a dietary fiber source, i.e., as a dietary supplement or a food additive.
Dietary fiber plays a strong supporting role in many nutraceutical foods where the fiber works in combination with health promoting ingredients such as nutraceuticals and antioxidants (Pszczola 1998). Glore, et al. 1994, reviewed the effects of pectin and other soluble dietary fibers on serum lipids and reported that in 88% of the 77 human studies, soluble fiber significantly lowered total serum cholesterol (TC). Of the studies that reported on the effect of a specific food or type of soluble fiber, beans and legumes reduced TC in 100% (10/10) and pectin reduced TC in 71% (10/14) of these studies. Hunninghake et al. 1994 and Kumar et al. 1997 found similar results. Judd and Truswell 1982 compared the effects of high methoxyl pectin with a degree of esterification (DE) of 71%, to low methoxyl pectin, DE 37%, and found both almost equally effective in lowering TC in humans. In 1980 Jeltema and Zabik reported on the pectin content of soybean hulls. In the water-soluble fraction they found about 0.5% pectin and 0.4% hemicellulose and in the water-insoluble fraction they found 7% pectin, 36% cellulose, 18% hemicellulose and 3% lignin. Gnanasambandam and Proctor 1999 reported on the X-ray diffraction and infrared spectra of laboratory extracted pectins. The specific cholesterol lowering ability of soybean pectin has yet to be established.
Soy, together with several other types of fiber, is being used in a wide variety of nutraceutical food products. Nutraceutical drinks and high fiber instant noodles use soy fiber to reduce fat and increase the health benefits from high dietary fiber levels (Pszczola 1998). A considerable amount of research done on the chemical analysis of pea hulls demonstrated that pea hulls alcohol insoluble residue (AIR) was 94% carbohydrate including 4 to 6% pectinaceous material (Weightman, et al. 1994). Functional properties of the AIR showed high cation exchange capacity and significant water holding and swelling capacities. Dalev and Simeonova, 1995 combined positively charged proteins below their isoelectric point with anionic pectin to produce stable, low oil emulsions for creams and mayonnaises with a high dietary fiber content. Low-methoxyl pectins have been studied as potential moisture barriers in edible coatings (Kester and Fennema 1986) and as low-calorie fat-replacers with improved mouthfeel in salad dressings, frozen deserts and baked goods (Glicksman 1991).
Most commercial pectin is extracted from citrus peel recovered after the juicing operation. Heat and mineral acids are used to solubilize the pectin and either alcohols or aluminum salts are generally used for precipitin. Commercial pectin is also extracted from apple pomace in a similar manner (May 1990). Both citrus peel and apple pomace are high in moisture and are typically dried within a few hours after the juicing operation to prevent attack by moulds and native pectic enzymes. There is an accompanying loss in pectin yield with drying, 15% to 30% for lemon peel (Crandall, et al 1978). A dry starting material like soy hulls and hypocotyls would be stable for long periods of time and not have the expense of needing to be dried, a distinct advantage.
Thus, there is a need in the art for pectins derived from other sources and especially pectins with improved color using a low value starting material such as soybeans and equipment that can be incorporated into existing soybean processing plants.